Fractures can provide flow paths from a reservoir to a wellbore or a wellbore to a reservoir. In general, permeability in a fracture is greater than in the material surrounding a fracture. Fractures may be natural or artificial. An artificial fracture may be made, for example, by injecting fluid into a wellbore to increase pressure in the well bore beyond a level sufficient to cause fracture of a surrounding formation or formations. The pressure required to fracture a formation may be estimated on a fracture gradient for that formation (e.g., kPa/m or psi/foot). Other techniques to make fractures can involve combustion or explosion (e.g., combustible gases, explosives, etc.). As to hydraulic fractures, injected fluid (water or other) aims to open and extend a fracture from a wellbore and may further aim to transport proppant throughout a fracture. A proppant is typically sand, ceramic or other particles that can hold fractures open, at least to some extent, after a hydraulic fracturing treatment. A proppant thereby aims to preserve paths for flow, whether from a wellbore to a reservoir or vice versa. Artificial fractures may be oriented in any of a variety of directions, which may be to some extent controllable (e.g., based on wellbore direction, size and location; based on pressure and pressure gradient with respect to time; based on injected material; based on use of a proppant; etc.).
Hydraulic fracturing is particularly useful for production of natural gas and may be essential for production of so-called unconventional natural gas. Worldwide reserves of unconventional natural gas are largely undeveloped resources. Reasons for lack of production from such reserves include an industry focus on producing gas from conventional reserves and difficulty of producing gas from unconventional gas reserves. Unconventional gas reserves are typically characterized by low permeability where gas has difficulty flowing into wells without some type of assistive efforts. For example, one of the principal ways to assist gas flow from an unconventional reservoir involves hydraulic fracturing to increase overall permeability of the reservoir.
Production of a resource from a reservoir typically commences with data gathering followed by modeling to simulate the reservoir and its production potential. A conventional simulator configured to solve a reservoir model may rely on information obtained through a well model where the well model is solved in a manner largely independent from the reservoir model. Where fractures are of interest, they are typically introduced into a reservoir model via finely spaced grids to account for the relatively small fracture dimensions and thereby generate a so-called reservoir-fracture model.
Various techniques described herein pertain to modeling of fractures, in particular, multiphase flow to, or from, a fracture. Various techniques described herein optionally allow for introducing fractures into a well model to create a so-called well-fracture model. For situations that call for reservoir modeling, a well-fracture model may be solved in a manner relatively independent of a reservoir model, which can alleviate a need for modeling fractures with finely spaced grids in a conventional reservoir-fracture model. In turn, a well-fracture model and reservoir model approach may decrease computational requirements when compared to a conventional well model and reservoir-fracture model approach.